1. Field of the Invention
This invention relates to a multi-channel reproducing apparatus and more particularly to an apparatus which is capable of reproducing a recorded information signal from each of a plurality of areas of a tape shaped record bearing medium extending in the longitudinal direction of the medium.
2. Description of the Related Art
In the field of magnetic recording, high density recording has recently come to be pursued. Video tape recorders (hereinafter referred to as VTRs) also have come to be capable of performing high density magnetic recording by lowering the travelling speed of a magnetic tape. The conventional method of recording an audio signal with a fixed head hinders efforts to have a high relative speed between the tape and the head and thus results in a deteriorated quality of reproduced sounds. In one of solutions of this problem, each of recording tracks which is to be formed by a rotary head is extended to be longer than the conventional track length and a time base compressed audio signal is recorded within the extended portions of tracks one after another. The details of this method are as follows:
For example, in the case of a VTR of the rotary 2-head helical scanning type, the magnetic tape which has been arranged to be wrapped at least 180 degrees around a rotary cylinder is changed to be wrapped to a greater (180+.theta.) degree around the rotary cylinder. Then, an audio signal which is pulse code modulated (PCM) and time base compressed is recorded within the additional wrapping portion of the tape thus obtained. FIG. 1 of the accompanying drawings shows the magnetic type transport system of a VTR of this type. FIG. 2 shows recording tracks formed on the magnetic tape by the VTR of FIG. 1. The illustrations include the magnetic tape 1; a rotary cylinder 2; heads 3 and 4 which are mounted on the rotary cylinder 2 at a phase difference of 180 degrees between them and are arranged to have different azimuth angles; video signal recording parts 5 of the tracks formed on the magnetic tape 1; and audio signal recording parts 6 of the tracks. The video parts 5 are formed with the heads 3 and 4 when the 180 degree wrapping portion of the tape around the rotary cylinder 2 is traced by these head. The audio parts 6 are obtained when the 8 degree wrapping portion of the tape around the cylinder is traced by these heads 3 and 4. In FIG. 2, reference symbols f1 to f4 denote the frequencies of tracking control pilot signals which are recorded in the recording tracks in a superimposed manner. These frequencies are in a relation of (f2-f1)=f3-f4.apprxeq.fH and f4-f2.apprxeq.2fH, wherein fH represents the horizontal scanning frequency of the video signal.
When the audio signal which is recorded in the audio part (or area) 6 in a state of having been pulse code modulated and time base compressed is reproduced, the sound quality of the reproduced audio signal favorably compares with the sound quality obtainable by an apparatus arranged specially for audio recording and reproduction.
For the VTR of the above-stated kind, there is another known method, wherein: A different audio signal is arranged to be recorded in the video part (or area) 5. FIG. 3 shows by way of example the tape transport system of an audio tape recorder of that method. The illustration includes a magnetic tape 1 and a rotary cylinder 2 which carries rotary heads 3 and 4. The heads 3 and 4 are thus arranged to obliquely trace the surface of the tape 1 to record an audio signal thereon. A time base compressed audio signal is recorded in each of a total of six longitudinally extending areas on the tape 1 every time the heads 3 and 4 revolve 36 degrees. An audio dedicated tape recorder which is capable of recording audio signals in six channels can be obtained by this arrangement. This tape recorder is further briefly described with reference to FIG. 4 below:
FIG. 4 shows recording tracks formed on a tape by the tape recorder. The audio signals are recorded in the areas (or channels) CH1 to CH6 while the head 3 or 4 is tracing the tape 1 from a point A to a point B, from the point B to a point C, from the point C to a point D, from the point D to a point E, from the point E to a point F and from the point F to a point G respectively. The audio signal recording can be accomplished in each of the areas independently of another. The audio signal recording is made in the so-called azimuth overlapping manner.
Further, in FIG. 4, reference symbols f1, f2, f3 and f4 denote frequencies of pilot signals recorded for the purpose of performing the known four-frequency tracking control.
FIG. 5 is a time chart showing the recording and reproducing operations of the tape recorder described above. In FIG. 5, a part (a) shows a phase detection pulse signal (hereinafter referred to as the PG signal) generated in synchronism with the rotation of the rotary cylinder 2. The PG signal is in a simple wave form of 30 Hz repeating a high level (hereinafter referred to as H level) and a low level (hereinafter referred to as L level) every 1/60 sec. A part (b) shows a PG signal of the polarity opposite to that of the PG signal (a). The PG signal (a) remains at an H level while the head 3 is rotating from the point B to the point G. The PG signal (b) remains at an H level while the head 4 is rotating from the point B to the point G. A part (c) of FIG. 5 shows a pulse signal for reading data obtained from the PG signal (a). The pulse signal (c) is provided for sampling the audio signal of a period corresponding to one field portion of a video signal (1/60 sec) for every other field. A part (d) of FIG. 5 shows a signal which is arranged to be at an H level to represent a signal processing period for adding an error correcting redundant code by means of a RAM or the like to one field portion of audio data sampled, for rearranging the sampled audio data and so on. A part (e) shows a signal which is arranged to be at an H level to represent a data recording period and is provided for the purpose of showing a timing for recording on the tape 1 the recording data obtained through the above-stated signal processing operation.
Referring to FIG. 5, the temporal flow of signals is as follows: The data sampled during a period between a point of time t1 and a point of time t3 (during which the head 3 is moving from the point B to the point G) undergoes the signal processing operation during a period between time points t3 and t5 (while the head is moving from the point G to the point A). The data thus processed is recorded during a period between time points t5 and t6 (while the head 3 is moving from the point A to the point B). In other words, the data is recorded then by the head 3 in the area CH1 shown in FIG. 4. Meanwhile, the data which is sampled when the PG signal (b) is at an H level, is also signal processed in the same manner before it is recorded by the head 4 in the same area CH1.
A part (f) of FIG. 5 shows another PG signal which is obtained by phase shifting the above-stated PG signal (a) to a predetermined phasic extent (36 degrees which is for one area, in this case). In cases where an audio signal is to be recorded according to this PG signal (f) and a PG signal which is not shown but is of the polarity opposite to that of the PG signal (f), the operation of the tape recorder is performed in the following manner: The data which is sampled during a period between time points t2 and t4 is signal processed during a period between time points t4 and t6 in accordance with a signal (g) which is as shown at a part (g) of FIG. 5 and is recorded during a period between time points t6 and t7 in accordance with a signal (h) shown at a part (h) of FIG. 5. In other words, the above-stated data is recorded in the area CH2 shown in FIG. 4 by the head 3 while the head 3 is tracing the tape from the point B to the point C. Then, data which is sampled during a period between time points t4 and t7 is likewise recorded in the area CH2 by the head 4.
A reproducing operation on a signal recorded in the area CH2 is as follows:
Data is read out from the tape 1 by means of the head 3 in accordance with the signal (h) of FIG. 5 during a period between the time points t6 and t7 (or t1 and t2). The data thus read out is signal processed in a manner reverse to the signal processing operation performed during recording. The signal processing operation is performed in accordance with a signal (i) shown at a part (i) of FIG. 5 during a period between time points t7 and t8 (or t2 and t3). During this period, error correction, etc. are performed. Then, in accordance with a signal (j) of FIG. 5, the signal processed data is produced as a reproduced audio signal during a period between time points t8 and t9 (or t3 and t6). Meanwhile, reproduction by means of the other head 4 is of course performed in a manner similar to reproduction by the head 3 at a phase difference of 180 degrees. With the two heads 3 and 4 used in this manner, a continuous reproduced audio signal is obtained.
It goes without saying that recording and reproducing operations can be accomplished for other areas CH3 to CH6 in the same manner by phase shifting the PG signal (a) to an extent of n X 36 degrees and by carrying out the operation on the basis of the phase shifted PG signal. Further, the operation can be carried out independently of the travelling direction of the tape.
As well known, in each of recording tracks formed within each of the areas, there are recorded additional data including synchronizing data, address data, CRC (cyclic redundancy check) data, error correcting parity data and ID data in addition to the 1/60 second portion of the audio data. With this tape recorder an approximately 90 minute length of audio signal can be easily recorded in each of the areas, so that sound recording can be made over a period of nine hours on a single piece of tape. As a result, however, it becomes virtually impossible for the operator to know what is recorded in which part of the tape. Conceivable solutions of this problem include a method of providing the so-called leader indexing arrangement for each of the areas. In accordance with this method, however, a look-up operation for a specific index must be repeated before reproduction of the record of a desired program. Such a look-up operation is quite troublesome for the operator. The method necessitates leader indexing for all the area Assuming that the tape is allowed to travel in the same direction for recording in all the area, it might be necessary in detecting the whereabouts of a desired program for reproduction to have the tape travel back and forth a maximum of six times from one end of the tape to the other end. Therefore, an extremely long period of time becomes necessary in searching for a desired program.